1. Field of the Invention
This invention relates to monochromatic and polychromatic display systems. In particular, this invention relates to display systems which provide matrix displays resulting from the conversion of long wave ultraviolet photons into visible light energy through the fluorescent excitation of fluorescent material compositions, such as synthetic Phosphors. In particular, this invention relates to displays where ultraviolet radiation is produced by the ionization of metal atoms through an electric field applied internal to minute cavities in the form of hollow cathodes. Still further, this invention relates to a display system where the long wave ultraviolet photons are directed in a constrained manner from one end of hollow cathode cavities for impingement through an ultraviolet transparent glass composition plate onto a fluorescent material composition.
2. Prior Art
Gas discharge display systems are known in the art. Although the subject display system cannot truly be classified as a gas discharge display, such gas discharge systems are believed to be the closest prior art to the subject system. In prior art gas discharge systems, a plurality of plasma displays may be attained either as alpha-numeric displays having generally linearly or arcuately segmented cathodes, or dot matrix displays. Such prior art systems are generally based on the ionization of a noble gas or gas mixtures. In such prior art systems, the ionization occurs between two flat and parallel electrodes with generally the anode electrode being transparent to light generated in the neighborhood of the cathode electrode.
Numerous disadvantages are apparent when such prior art gas discharge display systems are utilized. In such prior art gas discharge systems, the visible glow from the cathode surface is visibly stable only if the totality of the surface area of the cathode is uniformly covered by the glow and the cathode surface has uniform properties. In the event that either of these two conditions is not present, the visible light will provide a flickering effect which is deleterious to the eye of an observer.
Another major disadvantage of such prior art gas discharge systems is that the operating life of such prior art systems is dependent on the sputtering rate from the cathode electrode. This is due to the fact that the sputtering of the material from the cathode electrode generally deposits itself on the anode electrode, thus obviously reducing the anode electrode's transparency. The sputtering also reduces the gas pressure by physical adsorption of the filling gas. In order to provide an acceptable operating light of such prior art systems, such are generally operated at lower than maximum current density thereby resulting in only a less than optimum light output.
Some prior art work has investigated the generation of polychromatic systems based on the conversion of ultraviolet photons into visible light with Phosphor compositions. One such prior work is reported by V. Van Gelder, Proc. IEEE, Vol. 61, No. 7, July 1973, is directed to the utilization of ultraviolet photons emitted by recombinations in the positive column. In such prior work, the positive column is obtained through the well-known Principle of Similarity. In such prior systems, the gaseous discharge occurs in a tubular structure for the ion/electron recombination on the walls of the tubular structure. Additionally, such prior work based on the Principle of Similarity dictates relationship between the length, diameter and pressure of the tubular structure which is extremely difficult to produce. In normal tubes, the length/diameter ratio approximates 30.0 and such prior work dictates that such ratio should be preserved. Where the length in the tube in such prior work is two orders of magnitude smaller than an available fluorescent tube, in order to maintain the prescribed ratio, the diameter correspondingly must be two orders of magnitude less and the pressure two orders of magnitude larger than that found in an available fluorescent tubular structure. Such conditions would be extremely difficult to produce with the known technology, and at the present time are not capable of being manufacturable. Another disadvantage in such prior art theory is directed to the directionality of the system. In such prior art theory, the eye of the observer must be aligned with the axis of the tube in order to observe an optimized light intensity. A still further disadvantage of such prior art theory, is that as the resolution is increased resulting in the tube diameter decreasing, it is extremely difficult to coat the inner wall of the tube uniformly with the Phosphor composition.
Other attempts to generate polychromatic displays based on the conversion of ultraviolet photons into visible light relies on the negative glow of the cathode. Such prior art work in this field has been published by M. Fukushiwa, Digest SID, P.120, 1975. However, just as in the case of the positive column type prior work, the Phosphor composition in this prior art theory using the negative glow is also immersed in the gas plasma which results in similar disadvantages, as has been previously described for the positive column approach. Additionally, a lower efficiency in generating ultraviolet light in the plasma with flat parallel cathode-anode electrodes, the spectrum of the visible light released by the gas ionization does not consist solely of ultraviolet light, but rather the spectral lines produced in the visible spectrum prevent color purity and color saturation due to color mixing of gas and Phosphorspectra.
Other prior art gas discharge type displays using hollow cathodes are represented in U.S. Pat. No. 3,882,342; and U.S. Pat. No. 4,021,695. As in the case of other types of work, such references use the back filling gas to produce ultraviolet radiation in the positive column. This type of theoretical approach suffers the same disadvantages as has hereinbefore been described. In opposition, the subject display system does not require the gaseous medium to produce a measurable amount of ultraviolet energy. The gaseous medium in the subject display system is used to sputter the atoms of metal from the cathode and the applied electric field ionizes such atoms to produce an intense ultraviolet glow. Such an ultraviolet glow produced from the ionization of the metal atoms is much greater than the intensity of the ultraviolet glow from a gaseous medium.